Why Sleep?
Happy New Year! This year I am going to take a slightly different approach with my articles. Each month, I will choose a theme and then break that theme down into smaller, more concise sections. This will help me keep a more consistent schedule and might keep you more interested.
In January, I will discuss sleep. This week, I will give a broad-stroke overview of the stages of sleep and why they are important. In the following weeks, I will discuss different behavioral, natural, and technological changes that we can make to try to improve our sleep.
The timing of this theme of sleep is not a coincidence. I imagine that many of you reading this, just like me, stayed up late last night celebrating the new year. You might, just like me, have also had a couple of drinks to assist your celebration. Your new year celebration likely impacted your normal sleep-wake cycle and your quality of sleep. Sleep is very important for mental cognition, recall, development, and overall function. Along with mental health, sleep has a significant impact on your physical and emotional health. In another article, I will go into more detail on how behaviors like drinking and staying up late can hurt your sleep. In this article, I will discuss the different stages of the sleep-wake cycle and how those stages can impact your health.
Sleep-Wake Cycle
Healthy individuals naturally have a sleep-wake cycle that follows roughly 24 hours. This 24-hour cycle is commonly referred to as the circadian rhythm. A circadian rhythm is maintained through many different internal circadian clocks. Each circadian clock relies on different behavioral and environmental cues to decide if it is the appropriate time to be awake or asleep.
For example, we respond to natural light in our environment. Full Spectrum light from the sun tells us that it is time to wake up while low lighting and darkness tell us it is time to sleep. Another circadian clock we rely on is the build-up of adenosine in our brains. During waking hours, adenosine is slowly released in our brains. The longer we stay up, the more adenosine will collect in our brains. The build-up of this adenosine indicates when it is time to sleep.
Humans have many different circadian clocks, with many different cues. Each person will vary in sensitivity to each circadian clock and will process the cues from them differently. Therefore, each person has a circadian rhythm that is unique to them.
Our circadian clocks need to be “in beat” or synchronize with each other to keep our circadian rhythm. The phenomenon commonly known as jet lag is a great example of a dysfunctional circadian rhythm. When people are jet lagged, the circadian clock that relies on full-spectrum sunlight/darkness is not synchronized with the build-up of adenosine. As a result, people might have trouble sleeping at night or could be drowsy during the day.
Two main hormones control our sleep. First, melatonin is used to encourage sleep and gives us a feeling of drowsiness. Melatonin begins to be released when it gets dark, with levels peaking late at night or early in the morning. Second, cortisol is needed to counteract the effects of melatonin. Cortisol increases alertness and helps people wake up.
Stages of Sleep
There are 5 stages associated with full sleep: wake, N1, N2, N3, and rapid eye movement (REM). N1, N2, and N3 are progressively deeper stages of sleep with N3 being the deepest non-REM sleep. During a night of normal sleep, an individual will take 80-110 minutes to progressively go through all sleep stages to complete one sleep cycle. Sleep cycles will be repeated, going through each stage until the individual wakes up from sleep.
Wake
Wake is the first stage of sleep. This stage ranges from full alertness to the first few moments an individual closes their eyes. It is the only stage of sleep that can be skipped after the first sleep cycle.
N1-Light Sleep
N1 is the lightest stage of sleep. This stage consists of regular breathing and semi-rigid muscles. This stage lasts for a few minutes and consists of approximately 5% of total sleep.
N2-Moderate Sleep
N2 is the next deepest stage of sleep. During N2, your body temperature drops and your heart rate slows down. During the first round of sleep stages, this stage lasts for approximately 25 minutes and then it progressively gets longer with each stage of sleep. N2 makes up about 45% of total sleep. This stage is critical for memory consolidation and recovery. If you take a short 30-minute power nap, it will mostly be this stage of sleep. Taking power naps intermittently with studying could improve memory retention and recall. N1 and N2 are the best stages of sleep to wake up from because they will minimize mental fogginess and confusion.
N3-Deep Sleep
N3 is the deepest non-REM sleep and is often referred to as deep sleep. During N3 sleep, breathing and heart rate decrease dramatically. It is difficult to wake someone up from N3 sleep, but if someone is woken up during this stage, they can expect to feel mental fogginess and confusion for 30 to 90 minutes. If you feel extra tired after a full night of sleep, it is likely because you woke up during deep sleep. Deep sleep is a critical stage of sleep for mental and physical repair and recovery. During this phase, the body will repair tissue and grow bones. This stage lasts approximately 30 minutes and makes up about 25% of total sleep.
REM
REM sleep is classically characterized by rapid eye movement. This stage is the last in a sleep cycle and requires at least 80 minutes of sleep before it begins. During the first sleep cycle, REM lasts for about 10 minutes. Each cycle after that, REM gets a little longer and makes up about 25% of total sleep. REM sleep is associated with dreaming because it is the stage where the brain is the most active. To prevent sleepwalking while the brain is active, your skeletal muscles become atonic. REM sleep is also extremely critical in muscle repair, memory, and brain development.
So why are we discussing sleep in a health newsletter? Sleep is extremely critical to the development of your brain, skeletal muscle and bone growth, memory retention, prevention of chronic disease, and mood control. Without sleep, we could not function as humans, and with poor sleep, we are limiting our overall health and wellness. This newsletter’s focus was to establish a baseline understanding of sleep. Next week, we will discuss different behavioral tips to optimize our quality of sleep and get the most out of our rest.
Charest, J., & Grandner, M. A. (2020). Sleep and Athletic Performance: Impacts on Physical Performance, Mental Performance, Injury Risk and Recovery, and Mental Health. Sleep Medicine Clinics, 15(1), 41–57. https://doi.org/10.1016/j.jsmc.2019.11.005
Getting through exams: The power nap. (n.d.). Bright Network; Bright Network. Retrieved January 1, 2023, from https://www.brightnetwork.co.uk/making-most-university/power-power-nap/
How Sleep Works - Why Is Sleep Important? | NHLBI, NIH. (n.d.). Retrieved January 1, 2023, from https://www.nhlbi.nih.gov/health/sleep/why-sleep-important
How Sleep Works—Sleep Phases and Stages | NHLBI, NIH. (n.d.). Retrieved January 1, 2023, from https://www.nhlbi.nih.gov/health/sleep/stages-of-sleep
How Sleep Works—Your Sleep/Wake Cycle | NHLBI, NIH. (n.d.). Retrieved January 1, 2023, from https://www.nhlbi.nih.gov/health/sleep/sleep-wake-cycle
Mason, G. M., Lokhandwala, S., Riggins, T., & Spencer, R. M. C. (2021). Sleep and human cognitive development. Sleep Medicine Reviews, 57, 101472. https://doi.org/10.1016/j.smrv.2021.101472
Patel, A. K., Reddy, V., Shumway, K. R., & Araujo, J. F. (2022). Physiology, Sleep Stages. In StatPearls. StatPearls Publishing. http://www.ncbi.nlm.nih.gov/books/NBK526132/
PhD, K. K. (2022, April 25). REM Sleep: How to Speed Up Muscle Recovery. ACTIVE.Com. https://www.active.com/fitness/articles/rem-sleep
